The uptake of hydrogen by lanthanum pentanickel (LaNi₅) to form lanthanum nickel hydride (LaNi₅H₆) is
followed with three-dimensional imaging by neutron tomography. The hydrogen absorption process is
slower than the time needed for acquiring a single radiograph, about 10 s, but fast relative to the time
to acquire a fully-sampled tomographic data set, about 6000 s. A novel data acquisition scheme is used
with angles based upon the Greek Golden ratio, a scheme which allows considerable flexibility in
post-acquisition tomography reconstruction. Even with tomographic undersampling, the granular structure
for the conversion of LaNi₅ particles to LaNi₅H₆ particles is observed and visually tracked in 3D. Over
the course of five sequential hydrogen uptake runs with various initial hydrogen pressures, some grains
are repeatedly observed.